The present invention relates to an improved thermosensitive recording material which is capable of forming images with high image density in sharp contrast with the background by application of a relatively small quantity of energy thereto, and therefore which can be employed in highspeed thermosensitive recording apparatus, for example, for use in computers, facsimile apparatus and a variety of measuring instruments.
A thermosensitive recording material is a recording material comprising a support member, for example, paper, and a thermosensitive layer capable of forming a color upon application of heat thereto, which thermosensitive layer is formed on the support member. For the application of heat, for example, a thermal printer with a thermal head is employed.
At present, thermosensitive recording by use of the above-mentioned thermosensitive recording material is done in conjunction with the copying of documents and books and the recording of outputs from computers, facsimile apparatus and various measuring instruments.
For the above-mentioned applications, the thermosensitive recording materials, each comprising (1) a thermosensitive layer containing a colorless or light-colored leuco dye with a lacton ring, a lactam ring or a spiro-pyran ring, and an acidic material, such as an organic acid or a phenolic material, and (2) a support member for supporting the thermosensitive layer thereon, are now used in practice, since, with those thermosensitive recording materials, the developed images are clear and do not deteriorate with time, and those thermosensitive recording materials themselves can be stored for a long period of time without deterioration.
These days, the output speeds of the aforementioned recording apparatus employing the above-mentioned type of thermosensitive recording materials are being remarkably increased, almost day by day, together with the possible information density in the output.
In order to improve the thermosensitivity of thermosensitive recording materials for use in the above-mentioned thermal recording process, for example, the following methods have been proposed: In Japanese Laid-Open Patent Application Serial No. 52-106746, there are disclosed improved thermosensitive recording materials in which acetoacetic anilide compounds are contained for improving the thermosensitivity. In Japanese Laid-Open Patent Application Serial No. 53-48751, there is disclosed a thermosensitive recording material wherein a thermo-fusable material of which the melting point is in the range of 60.degree. C. to 200.degree. C. is contained at least in either the basic dye or the coloring material in the thermosensitive layer of the thermosensitive recording material. Furthermore, in Japanese Patent Application Ser. No. 52-20142, there is disclosed a method of producing a thermosensitive recording material with its development capability improved by treating the surface of its top layer in the range of 200 to 1,000 seconds in terms of Beck Smoothness Degree.
These thermosensitive materials are still not satisfactory for practical use.
As other thermosensitivity improvement agents, the following are known:
Fatty acid amides compounds, such as acetamide, stearic acid amide, linolenic acid amide, lauric acid amide, myristic acid amide, hardened beef fatty acid amide, palmitamide, oleic amide, rice bran fatty acid amide, coconut fatty acid amide, methylol compounds of the above-mentioned fatty acid amides, methylenebis(stearamide), and ethylenebis(stearamide).
When the above-mentioned thermosensitivity improvement agents are employed in the thermosensitive recording materials and thermal recording is performed for a long period of time by a thermal head, those thermosensitivity improvement agents produce dust on the thermal head during the recording process, causing the thermal head to stick to the thermal recording material, hindering its scanning operation along the surface of the thermal recording material and making the developed images unclear. Therefore, it is necessary to clean the thermal head from time to time.
Under such circumstances, a thermal recording process capable of recording images at a high speed continuously for a long period of time, without accumulation of dust on the thermal head during recording the images on a thermosensitive recording material, and therefore without the necessity of cleaning the thermal head, is desired.
Furthermore, the conventional thermosensitive recording materials have additional shortcomings in that fog occurs during storage thereof, and when pressure is applied to the recording materials or when the recording materials are subjected to surface friction, the affected portions of the recording materials are discolored.